This invention relates generally to an improved loading dock leveler lift assembly which employs a pivotally mounted deck to angularly adjust to the level of variously sized vehicles parked adjacent a loading dock, and a mechanism for adjusting the deck to selected raised and lowered angular positions as well as lift and descent positions while the deck is maintained in a horizontal position. The invention further relates to a method for operation of such an improved dock leveler lift assembly.
Loading dock facilities often employ two types of devices to facilitate loading and unloading of various sized vehicles; namely, dock levelers and dock lifts. Examples of dock levelers are disclosed in U.S. Pat. Nos. 3,583,014, 3,699,601, 3,728,753, 4,110,860, 4,257,137, 4,531,248, 4,570,277 and 4,744,121. Such dock levelers compensate for height variations between the bed of a vehicle parked on a roadway adjacent to the dock and the platfor surface of the dock by employing a deck which is hingedly connected at its rear edge to a frame mounted within a pit formed in the dock and open at the front and top sides. The deck is pivoted between a raised, or upwardly inclined, position above the dock platform surface and a lowered declining position below dock level to allow loading and unloading of vehicles which have beds above or below the platform surface of the dock. An extension plate, or lip, is hinged to the front edge of the deck and is movable to an extended position to bridge the space between the rear edge of the bed of the parked vehicle and the front edge of the deck. Such dock levelers are not designed to be used to transfer personnel and material handling equipment between the loading dock surface to the roadway since the typical height between the dock surface and the roadway provides a slope greater than the slope across which personnel and material handling equipment may safely travel.
Loading docks are also situated where it is sometimes necessary to transfer material between the loading dock surface and the roadway. In such situations materials may be temporarily stored outside the loading dock facility on ground-level storage areas or in separate buildings, or when side loaded vehicles cannot be parked with their side loading surface adjacent the loading dock. Another such situation involves vehicles having low beds which cannot be reached by operation of conventional dock levelers. Some loading dock facilities provide for these circumstances by using dock lifts having vertically adjustable horizontal platforms for raising and lowering personnel and equipment between dock level and the roadway. Other dock facilities utilize a stationary, long, sloping ramp leading from the platform surface of the dock to the roadway.
Dock lifts have heretofore been provided which move vertically while maintaining a horizontal platform surface and also allow adjustment of the platform or deck to an upwardly inclined position relative to a reference level or plane. Two examples of such lifts, called bi-elevational platform lifts, are disclosed in U.S. Pat. Nos. 4,221,280 and 4,394,888. One drawback of such bi-elevational platform lifts is their inability to allow adjustment of the platform to both an upwardly inclined position and a lowered declining position relative to one reference level, such as the surface of the loading dock. Thus, these devices cannot function in the same manner as the conventional dock levelers described above.
It is desirable therefore to provide a single device for facilitating the various loading and unloading operations performed at loading dock facilities and thus remove the need for installing multiple devices which perform a few but not all of the important functions. A method for operating such a single device is also desirable. It is also advantageous to eliminate the need for long stationary ramps leading to the platform surface of the loading dock particularly where space at the loading dock is at a premium.